It is well known that certain materials possess piezoelectric properties such that when an electric potential is applied, a mechanical stress is produced within the material causing it to deflect. Such materials include simple naturally occurring and artificial crystals, and more sophisticated artificial ceramic materials.
One application of such piezoelectric materials is as valve actuators. In such applications, thin sheets of piezoelectric ceramic material may be laminated to an electrode sheet. A monomorph is an electrode sheet with a piezoelectric layer on one side. A bimorph has piezoelectric layers on both sides. A cantilever-fashion piezoelectric valve has an actuator in which one end of a piezoelectric material beam is securely clamped, and application of electric potential to the clamped end causes the free end to deflect with respect to a valve seat to prevent or enable fluid flow through the valve seat.
Generally, prior piezoelectric actuated valves have been designed for very specific applications, and as such, either have incorporated significant application-specific internal structure, e.g., U.S. Pat. No. 4,492,360 to Lee, II et al., or have been part of a significantly more complex larger structure, e.g., U.S. Pat. No. 4,340,083 to Cummins. Besides being suitable for only a narrow range of applications, the structural complexity necessary substantially affects the manufacturing complexity and disadvantageously increases the cost required to produce such valves.
Another consideration in the field of piezoelectric valves is the tradeoff which must be made between actuator force and physical displacement--a cantilevered piezoelectric actuator has a decreasing linear relation between the force that the actuator can apply, and the physical displacement of the end of the actuator. For example, maximum force may be produced when the actuator displacement is zero, in which case, force decreases linearly with displacement. Thus, a design tradeoff must be made since a non-zero force must be applied to seat the free end of the actuator on a valve seat without having leakage. Because of the force-displacement relationship, this non-zero force translates into a maximum distance that the free end of the actuator can sit above the valve seat. On the other hand, to open the valve, the free end of the actuator must be some minimum distance above the valve seat to obtain maximum fluid flow through the valve.
The difference between the maximum and minimum distances that the free end of the actuator can sit above the valve seat is typically relatively small, e.g., .about.100 microns. This presents a difficult problem for low-cost manufacturing where dimensional tolerances tend to be fairly large. As a result, complicated assembly procedures and/or additional structure have typically been required, which in turn increase the manufacturing cost.